The present invention relates generally to span lock systems for single and double leaf drawbridges; and more particularly to a novel and improved span lock centering guide and mounting in a single or double leaf drawbridge.
Span lock systems, in addition to securing the leafs of a drawbridge in the closed position, also provide for vertical shear load transfer between their outer ends whereby the leaf tips deflect uniformly during passage of vehicular traffic. U.S. Pat. No. 5,327,605 to Robert L. Cragg discloses such a system in which a rectangular lock bar, retractable parallel to the drawbridge span length, fits through a guide mounted on a rectangular base on the outer end of one leaf of the bridge and into a receiver mounted on a rectangular base on the outer end of the other leaf. The bases are secure to the bridge structure by bolts which are spaced apart along the top and bottom edges of both bases, and along the edge of the receiver base away from the outer leaf end. Stiff annular springs are vertically supported by guide pins which are fixed to the wear shoes with sliding clearance in the guide and receiver, respectively. The springs urge the wear shoes in firm and continuous contact against the lock bar. The top and bottom surfaces of the lock bar and the shoes at their confronting outer ends are beveled to accommodate slight vertical misalignments between the guide and receiver during insertion of the lock bar. In a fully locked position, vertical shock loads to the bar from road traffic are cushioned by the springs, and uncontrolled bounce of the leaf ends is eliminated. The sides at the outer ends of the lock bar are also beveled to accommodate slight lateral misalignments, but there are no provisions for limiting shear stresses in the lock bar from more severe lateral misalignments as may occur due to wind, thermal expansion, uneven wear, uneven settlement of bridge structure, or marine vessel collision.
While the span lock system of U.S. Pat. No. 5,327,605 has distinct advantages over prior art designs for cushioning vertical shock loading, it does not limit horizontal bending and shear stresses in the lock bar due to substantial lateral misalignment of the span leaf locking elements as may occur due to side winds, thermal expansion or contraction, uneven settlement of bridge structure, or marine vessel collision.
U.S. Pat. No. 2,610,341 to Gilbert discloses a span lock system with means for horizontally aligning the leafs of a double leaf bascule bridge but does not limit horizontal bending or shear stress in the lock bar lock. A slotted alignment disc is loosely rotatable within a male member at the tip of one leaf. A lock bar reciprocates lengthwise on an axis normal to the bridge span in a receiving member at the tip of the adjoining leaf includes and engages the slotted disc. The receiving member includes a vertical slot slightly flared at the upper and lower ends for capturing the male member and laterally positioning the alignment disc along the length of the lock bar.
Accordingly, it is an object of the present invention to provide a centering guide for a span lock system in a single or double leaf drawbridge which will limit horizontal misalignment of the locking components.
Another object of the invention is to limit the horizontal stresses transferred to the lock bar in a span lock system as may occur due to strong side winds, thermal expansion or contraction, uneven wear of bridge components, or uneven settlement of bridge structure.
Another object of the present invention to provide a mounting for a span lock with a centering guide in a single or double leaf drawbridge which will maximize the ability of the wear shoes to accept misalignments of the wear shoes experienced during passage of heavy traffic on the bridge leafs.
Still another object of the invention is to provide a centering guide for aligning locking components in span lock system which is of relatively simple design for facilitating ease of manufacture, maintenance, repair and replacement of parts.
These and other objects and advantages of the invention are accomplished by a span lock centering guide and mounting in a drawbridge. A guide housing mounted on either side by two columns of bolts to the outer end of one leaf of the bridge includes an opening with vertically opposed cushioned wear shoes slidably supporting an elongate lock bar reciprocative lengthwise in a direction along the length of the drawbridge. A receiver housing mounted by two columns of bolts to the outer end of the other leaf is positioned to interlock with the guide housing and includes a like opening slidably receiving the lock bar between vertically opposed cushioned wear shoes. A pair of springs, spaced apart along the length of the lock bar, in each housing, urge the shoes in continuous contact with the upper and lower surfaces for reducing shock loads and eliminate bounce of the leaf ends. Each spring comprises a stack of coaxial Belleville discs retained by a cylindrical guide pin fixed to the wear shoes and is slidable in the housings. The center lines of the guide pins are parallel to and substantially between the center lines of the bolt columns. A pair of vertical guide columns project from either side of the guide housings opening with the upper and lower ends of the distal sides tapering inwardly, and another pair of vertical guide columns project from the on either side of the receiver housing opening with the upper and lower end of the proximal sides tapering outwardly. Within a specified maximum limit of misalignment, the guide and receiver columns interengage causing their openings to closely align and facilitate insertion of the lock bar into the opening of the receiver housing with limited horizontal bending and shear. The distance between the proximal sides of the receiver housing exceeds the distance between the distal sides of the guide housing for specified maximum misalignment.